Life Expectancy and the Life Span

Two thousand years ago, in ancient Rome, the life expectancy of a newborn child was just 22 years. The life expectancy of a child born in the 1800s in Europe equaled 35 years. In the United States in 1900, life expectancy was approximately 47 years. But these figures do not mean that the average adult during these eras died at these ages. Life expectancy refers to demographic projections about the average length of life. And unless otherwise stated, the age reported represents life expectancy at birth for any given era.

Life expectancy at birth has increased significantly over the past century, and it varies by gender, ethnic, and racial groups. In 2002, the National Vital Statistics Reports published life expectancy projections for the year 2000 (Arias, 2002). In the United States, White males born in the year 2000 could expect to live 74.8 years, Black males 68.2 years, White females 80 years, and Black females 74.9 years. As can be seen from these figures, life expectancy at birth in the United States has risen approximately 25 years since the 47 years reported for 1900. Data such as these are sometimes interpreted to mean that as a population, we are living significantly longer into advanced old age. But this interpretation is not entirely correct. The main reason for the increase in life expectancy at birth over the past century is that the infant mortality rate decreased significantly during the same time. That is, more children are reaching adulthood than ever before. Once we become adults, however, life expectancy for any given age has changed much more modestly. Demographers often use age 65 to examine changes in adult life expectancy. For example, from Arias's (2002) report, life expectancy at age 65 in 1950 in the United States was 13.9 years and in 2000 was 17.9 years, an increase of 4 years.

The Belgian statistician Quetelet (1842) is generally regarded to have published the earliest life expectancy data available. Quetelet reported that life expectancy at age 65 in 1830s Europe was slightly greater than 10 years. So, over approximately 170 years, life expectancy at age 65 has increased a little more than 7 years. Quetelet's estimations were calculated the same way they are today. That is, life expectancy refers to the age at which half a given population group is expected to be living and half are expected to have died.

Apart from life expectancy, life span is defined as the maximum age that a person can live without illness or accident. Hayflick (1977) and his associates have demonstrated that normal human cells survive and reproduce for a certain period but eventually enter a period of degeneration and die. On the basis of his evidence, Hayflick has estimated the maximum potential life span at about 110 years. From this point of view, if all pathological causes of death were eliminated, including cancer and heart disease, a human would still die, merely as a result of the programmed life span of cells and the number of times they are capable of reproducing. Using a somewhat different approach, a more recent series of analyses by Olshansky and colleagues has reached similar conclusions regarding the potential length of the human life span (see, for example, Olshansky, Carnes, & Cassel, 1990).

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